1. Field of the Invention
This invention relates to a knife assembly and is more particularly concerned with a knife assembly designed to be incorporated into a shredder for comminuting industrial waste and other such material.
2. Description of the Prior Art
Knife assemblies have been extensively used in comminution devices, such as shredders for industrial waste, meat cutters, ice breakers, and similar devices. These knife assemblies are usually adapted to be received on a drive shaft, which rotates to turn numerous, spaced knife assemblies about an axis. The individual knife assemblies previously employed have comprised various configurations, depending upon the material to be comminuted and the size of the desired final product. U.S. Pat. No. 4,678,126, discloses one such knife assembly and its incorporation into a shredder. The knife assembly disclosed therein employs two curved knives spaced on opposite sides of a central collar. The knifes curve in the same circumferential direction about a central axis. Numerous knife assemblies are arranged in spaced relationship along an arbor, with their respective points disposed in helical relationship. The spaced knife assemblies cooperate with a fixed anvil having a plurality of grating members, to shred waste material.
The knife assemblies are arranged so that the leading edge of the point, or tooth, moves past a grating member before the curved shredding portions, thereby forcing material towards the arbor body. Should the knife assemblies be unable to cut through the material, jamming the shredder, control means will reverse the rotation of the arbor in an attempt to unwedge the tooth. During this reversed rotation, however, no cutting or shredding can be accomplished, since the knives of the knife assemblies are all radially curved in the same circumferential direction. Consequently, the rotation of the knife assemblies must then again be reversed in an effort to cut the jamming material, since there are no secondary knives curving in opposite direction as that of the principal knives.
Another problem is encountered in industrial shredders having inwardly counterrotating clawing assemblies, when large objects are introduced into the feed bin. If the exterior surface of the material is too large, the counterrotating knife assemblies often cannot nip the object to draw the object between the knives. Consequently, the object will often ride above the counterrotating knives. Conventional shredders of the prior art have no means to reorient the objects in the feed bin when the rotation of the knife assemblies is reversed.
U.S. Pat. No. 4,538,766, discloses a knife assembly having a generally L-shaped cutting surface and an arcuate trailing edge. In one embodiment, a plurality of knife assemblies are spaced along a drive shaft and rotated to turn between calibrated slots defined by a stationary element. The knife assemblies include one knife blade only, and the cutting action is similar to that disclosed in U.S. Pat. No. 4,678,126. A second embodiment employing knife blades arranged on outwardly counterrotating shafts is also disclosed. The material is not cut between the knife assemblies of the two counterrotating shafts, but is instead comminuted between the knife assemblies and a stationary element, as in the first embodiment. Even if the rotation of the drive shafts is reversed, no comminution between the counterrotating knife assemblies is possible, since the knives curve in only one direction, defining a single cutting surface. This limits the cutting action to be in this one direction only, and in cooperation with a stationary member.
U.S. Pat. No. 2,551,049, discloses a multiblade rotary gang for a mincing operation in a meat cutting machine. The two-blade cutters disclosed in one embodiment employ two straight-edged blades spaced around the periphery of a center piece. In a second embodiment, the two-blade cutter employs conventional, curved cutting edges which extend radially and curve in the same circumferential direction around the center piece.
Other knife assemblies previously used, employ various curved shapes defining a cutting edge. No known assemblies, however, include a secondary knife curved in the opposite direction as the principal knife for accomplishing continued cutting and reorientation of the material when the rotation of the assemblies is reversed.